Most sports nutritionists rate creatine monohydrate as the most effective performance-enhancing supplement.  In ‘responders’ to creatine, it increases strength, power, muscle mass, and performance in repeated bouts of high-intensity exercise.  It works mainly by increasing creatine phosphate (CP) levels in muscle and possibly by triggering chemical pathways in muscle that cause protein synthesis.  CP is a high energy compound used to restore muscle adenosine triphosphate (ATP), which is vital to exercise performance and life.  Andrew Jones and colleagues from Exeter University in the U.K. showed that five days of creatine-loading (5g, four times per day) increased muscle CP by 8 percent.  Curiously, creatine slowed the rate that CP resynthesized ATP.  Body processes always seek a balance and try to operate at the lowest possible energy level.  The body compensates for increased muscle CP resulting from creatine supplementation by slowing metabolic processes.  The muscles have a greater energy capacity, so they don’t have to work as hard.  (American Journal of Physiology:  Regulatory Integrative Comparative Physiology, 296:  R1078-R1087, 2009)